merlion-node-exporter-cpp

Modern C++23 reimplementation of the Prometheus node_exporter — hardware and OS metrics exposed by *NIX kernels, in a single statically-linked binary.

This is the C++ sibling of merlion-node-exporter-rs, following the same dual-language pattern as merlion-tsdb-cpp / merlion-tsdb-rs. Both exporters expose the same Prometheus text-format on /metrics and use byte-identical metric names, so they are drop-in replacements for each other — and for upstream node_exporter — from a scrape / dashboard / alerting standpoint.

The installed binary is named merlion-node-exporter (no language suffix) — pick the implementation that matches your build toolchain; operators run the same command either way.

Status — design-stage. The architecture, dependency choices, file layout, and interface signatures are pinned in docs/DESIGN.md. The CMake scaffold builds an empty binary today; implementation is tracked in the Implementation Plan.

Why a C++ version too?

merlion-node-exporter-rs is the primary implementation today. The C++ sibling exists for the same reasons as merlion-tsdb-cpp:

1. Toolchain reach. Some deployment environments standardise on a C++ toolchain (LLVM-only fleets, vendored CMake superbuilds, embedded targets) and a parallel C++ implementation lets those environments adopt Merlion without dragging in a Rust toolchain.
2. Cross-checking. Two independent implementations of the same wire protocol catch ambiguity bugs in the spec itself.
3. Design discipline. Forcing every collector to express the same metric in two languages keeps the metric-naming contract honest.

Tech stack

Concern	Choice	Why
Language	C++23	std::expected, std::format, designated init, modules-ready
Compiler	Clang 18+ (Homebrew LLVM on macOS)	Matches the rest of MerlionOS
Build	CMake 3.28+	FetchContent makes deps trivial
HTTP	cpp-httplib	Header-only, blocking, perfect for per-scrape exporters
CLI	CLI11	Header-only, idiomatic
Logging	spdlog	Mirrors the tracing setup in -rs
Tests	Catch2 v3	Fixture-friendly
Format	clang-format	Pinned config in .clang-format

See docs/DESIGN.md for the rationale on each choice and for the full file/module breakdown.

Quick start

brew install llvm cmake
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
./build/merlion-node-exporter --web.listen-address :9100

On macOS, point CMake at Homebrew LLVM explicitly if cc/clang++ on your $PATH is still Apple Clang:

export CC="$(brew --prefix llvm)/bin/clang"
export CXX="$(brew --prefix llvm)/bin/clang++"

Roadmap

Mirrors merlion-node-exporter-rs's roadmap exactly — same Linux MVP scope (~15 collectors), same metric names, same CLI flags. See docs/DESIGN.md#implementation-plan for the ordering.

Development

cmake -S . -B build -DMNE_BUILD_TESTS=ON
cmake --build build -j
ctest --test-dir build --output-on-failure
clang-format --dry-run --Werror $(git ls-files '*.cpp' '*.hpp')

License

Apache License 2.0 — see LICENSE and NOTICE. Metric names and CLI flags follow upstream node_exporter for compatibility.